In sewing applications such as the automated stitching of repeated discrete patterns onto fabrics, it is frequently necessary, upon completion of the sewing of one pattern, to tack or repeat sew the thread at the tail end of the pattern and then advance the sewing needle to the beginning of the next pattern, and to trim the thread between the two patterns, particularly on the front or visible face of the fabric.
In the manufacture of quilted fabrics in which, for example, a cover, a liner and one or more layers of filling material are joined to form an article such as a quilted furniture or mattress cover, automated sewing machinery is commonly employed to sew the layers of material together, with stitching applied in repeated patterns, or arrays of repeated patterns. High speed and economic production of such quilted fabrics generally requires equipment utilizing entire arrays of needles, ganged together and driven through a common stitch forming mechanism, to apply a plurality of patterns simultaneously in a predetermined array. Frequently, the preferred stitch for this purpose is a chain stitch such as a standard 401 double lock chain stitch. Usually, running lengths of these quilted fabrics are sewn and wound into rolls and subsequently cut to size. The double lock chain stitch is preferred for this purpose because it is elastic, and does not unravel or run when cut.
Machines for sewing double lock chain stitches employ three stitch forming elements to guide and loop the threads in the formation of a stitch. One of these elements is a needle, which cyclically reciprocates through the fabric, usually from above a fabric as it is moved over a horizontally disposed needle plate, for feeding loops of a top or needle thread, carried by the needle eye, through the fabric. The second element is conventionally referred to as a looper, which oscillates in synchronism with the needle and applies a bottom or looper thread from below the plate by feeding loops of a looper or bottom thread through the needle thread loop as the needle descends below the plate on which the fabric is supported during each stitch cycle. The third element is commonly called a retainer, which moves horizontally in a cyclic motion in a plane below the plate and between the other elements to guide or horizontally displace a portion of the threads to spread the threads, allowing the descending needle to pass through a portion of the previous stitch, to thereby allow the consecutive stitches to be formed in a characteristic interlocking manner.
The more desirable automated quilting machines for quilting in patterns provide structure for supporting multiple sets of the stitch forming elements in arrays that correspond to the spacing of the patterns to be formed on the fabric. Preferably, the arrays in which the elements are supported can be selectively rearranged on with equipment that provides for a plurality of element mounting positions disposed in a closely spaced matrix. Such positions must be closely spaced to allow for flexibility in the layout of a multiplicity of pattern arrays, as well as to sew patterns with relatively close spacing.
Where discrete or disconnected patterns are to be sewn, trimming of the threads is highly desirably, particularly on the front or visible face of the fabric. In machines with single needle mechanisms, solenoid actuated thread cutoffs can be employed, but in the ganged multi-needle chain stitch machines, particularly those in which the sewing element sets are disposed closely or in reconfigurable arrays, where the elements are either many in number or must be easily rearranged, thread trimming has been accomplished downstream of, and subsequent to, the sewing operation, and often by hand.
Accordingly, there is a need for a method of efficiently trimming the threads in an automated quilting process and for a simple, compact and efficient apparatus for trimming threads, particularly where multiple discrete double lock chain stitched patterns are to be automatically sewn in arrays.